1. Field of the Invention
This invention relates to high frequency energy devices operable at microwave, millimeter wave, infrared and optical frequencies wherein an interchange of energy takes place between a stream of charged particles and an electromagnetic wave in a waveguide, and more particularly to such devices wherein the electromagnetic wave extracts energy from an electron beam as it propagates on the beam within the waveguide.
2. Discussion of the Prior Art
Microwave amplifiers that utilize an electron beam to achieve amplification have essential parts that comprise these devices. That is, means of generating, directing, and collecting the electron beam are essential. Typically, an electron gun, magnetic or electrostatic focusing field, and a collector serve the above purposes. In conjunction with an electron beam is a means for translating i.e. propagating, an RF energy wave in the vicinity of the electron beam in order to obtain an interaction between beam and wave for the purpose of amplifying the RF energy in the wave. RF amplifiers such as traveling wave tubes (TWT), klystrons, and crossed field amplifiers (CFA) use various structures such as the helix, ring-bar, ring-loop, cavities, meander lines, vanes, etc. to translate or propagate the RF energy which velocity modulates, i.e. bunches, the electron beam in the vicinity of the RF wave field. The primary differences in these types of amplifiers are the strength and time duration of the RF fields for bunching the electron beam and spatial characteristics of the beam.
The construction of the traditional slow-wave high power microwave tube becomes increasingly difficult and more expensive with increasing frequency. Consequently, at mm wave frequencies, the devices are prohibitively expensive and the RF performance characteristics are degraded.
Another class of devices worthy of mentioning are the so-called space charge amplifiers that also depend on space charge bunching phenomena for their functioning. These devices include velocity-jump, space-jump and scalloped-beam amplifiers. What is characteristic about these types of apparatus is that they do not depend upon RF guiding structures, which makes them relatively simple to construct. Application of these devices have been limited, however, because of their focusing difficulties, higher order mode generation and low gain per unit length. Recent interest in the millimeter (mm) wave range of the electromagnetic spectrum has generated added interest in the space charge amplifiers based on new interaction mechanisms which show promise of producing practical devices.
In the field of gyrotron technology, devices employing relativistic interaction mechanisms have obtained impressive RF output power and efficiency. However, the very high voltages and high magnetic fields which require superconductive solenoids are not attractive features for light weight mm wave amplifiers for airborne and tactical applications.
Known prior art patents and publications of interest include: U.S. Pat. No. 3,129,356 issued to R. M. Phillips for a "Fast Electromagnetic Wave And Undulating Electron Beam Interaction Structure"; U.S. Pat. No. 3,118,083 issued to E. A. Ash for a "Cyclotron Wave Harmonic Generator"; an article in IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-25, No. 6 June, 1977, pages 561-563 by J. E. Walsh, et al. entitled "Relativistic Electron-Beam-Generated Coherent Submillimeter Wavelength Cerenkov Radiation"; an article in Physics Today, December, 1962, pages 38-42, by N. Marcuvitz entitled "Propagation of Waves in Plasma"; a survey article from Varian Associated, Inc., pages 234-237, by H. R. Jory et al. entitled "Gyrotrons for High Power Millimeter Wave Generation"; and a news note in Industrial Research, July, 1976, p. 14, on "Lasers-electron Beam Amplifies Laser".
It is, therefore, an object of this invention to provide an improvement in relatively high frequency amplifier type devices.
It is another object of the invention to provide a device for microwave, millimeter wave, infrared and optical frequency applications that is relatively simple and inexpensive to manufacture, yet is free from circuit and power limitations imposed by known slow-wave devices and free from high voltage and high magnetic field limitations imposed by known fast wave devices.